Summary

This is the first article in a series about my journey implementing PSoC 6 SDK libraries for the Maxxim One Wire Bus and the DS18B20 temperature sensor.

As you can see there will be many parts to this story:

Story

I recently got a twitter message from a gentleman named “Neeraj Dhekale”.  He asked about a library for a one wire sensor for PSoC, actually to be specific he asked about a component for a PSoC 4.

Then I asked him what sensor and responded that he wanted to use the Maxxim DS18B20 temperature sensor.

This sensor is a one wire temperature sensor, here is a bit of snapshot from the data sheet.

After reading the data sheet I decided that I really didn’t want to implement a complete library for this sensor.  So, I started looking around for a driver library.  After googling around a little bit I found a library on GitHub (https://github.com/DavidAntliff/esp32-ds18b20) which looked promising, even though it is ESP32 specific.

But, after looking at this GitHub library a bit, I decide to start from there.

Before I get started two comments.

  1. He asked for PSoC 4 … but I am going to do PSoC 6 (because I can use Modus Toolbox).  There is no reason why this wouldn’t work on PSoC 4 – but it would take a bit of work
  2. I can’t think of a good reason to use 1-wire, it sure seems like I2C would be simpler

Build a Base Project

I start this whole effort by creating a new project for the CY8CKIT-062S2-43012 (because that happens to be the kit on my desk at the moment)

I will use the IoT Expert FreeRTOS Template project

For debugging this whole thing I will use a command line shell.  To get this into the project I add the ntshell library. Run “make modlibs” to start the library manager.

In the library manager pick the “ntshell” library

To develop this project I want to use Visual Studio code.  So, I run “make vscode” (to create the configuration files) and start vscode by running “code .”

When VSCODE starts up it looks like this:

In order to use the ntshell library you need to shuffle the files around a little bit.  Move the ntshell.h/.c into the main project by doing a drag/drop in the explorer window.

It will ask you really want to move the files

Once it is done, the ntshell functions which you need to customize will be part of the project.

To use the ntshell, you need to add the task to main.c

And start the task

Build and compile

And you should have a working project.

Run “make program” to get the board going

And you should have a working project (with a blinking led and a command line)

Add the DS18B20 Library

Now that I have a working project the next step is to clone the DS18B20 library into my project.  This is done using

  • git clone https://github.com/DavidAntliff/esp32-ds18b20

The next step is to establish how bad things are with the new library.  So run the compiler.

When I look at the ds18b20.c file I can see that there are some obvious problems

Fix those:

Run the compiler again.  Now I am missing owb.h which is the public header file for the one wire bus.

I now make a directory to hold the new owb files called “p6sdk-onewire”.  Then I add a file “owb.h” (as a blank file)

When I run the compiler again, there are now two classes or error … owb and esp32 logging function. Here is an example of the ESP_ problems.

And here is an example of the owb problems.

To make this thing go, I edit ds18b20.c file and add logging templates (just stub functions that don’t do anything)

Create owb.h

If I was smart, I would have started with David Antliff “owb” library.  But I don’t.  What I do is search through “ds18b20.c” and find every function call to owb_ and then copy those function calls into owb.h (my new file).  Then I fix the function calls to have correct prototypes based on what I see in the ds18b20 library.  Here is what my owb.h file looks like after that process.

When I run the compiler again things look way better (just some complaining about const datatypes) and a complaint about the include path.  The include path thing is visual studio code not knowing that I added a new directory called p6sdk-onewire.

To fix the include path I run “make vscode” which tells VSCODE about the new directory.

That is a good place to split this article.  In the next article I will add functions to read and write the bus.

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